Transportation costs of obesity

Recently someone asked about the amount of energy Americans are storing in body fat. A more pertinent question is how much energy is wasted hauling that fat around. Cars, planes, and trains have to burn extra fuel to move the excess pounds. How many barrels of oil would America save if not for all that lard? -- Scott Sanders, St. Louis

Considered individually, the cost of hauling Joe and Mary Chub from point A to point B is relatively small, and in fact could have a positive socioeconomic impact if airlines were to wise up and charge by weight. From a macro perspective, however, we need to realize Americans collectively are carrying an extra 4.6 billion pounds of fat, one more reason the lean, hungry nations of the world are gaining on us fast.

According to a study sponsored by the Aluminum Association, a 20 percent reduction in a small car's weight can result in a 10 percent increase in fuel economy. However, clearly what the aluminum people had in mind was making cars out of lighter materials (presumably aluminum), not getting the occupants to lose weight. A typical small vehicle weighs 2,900 pounds, so a driver carrying an extra 20 pounds adds less than 1 percent to the car's mass.

That doesn't tell you the whole story, though. A 2009 paper by the environmental research group Resources for the Future suggests fat drivers tend to buy fat cars-that is, ones that are larger and less fuel-efficient. The authors estimate that if overweight and obesity rates had stayed at 1980 levels-20 percentage points lower than now-consumers in 2005 would have bought vehicles whose fuel economy on average was 1 MPG better than the ones they did.

This is useful information. Rather than scolding people for buying SUVs because they're bad for the environment, one might more effectively advance the argument that an SUV proclaims the owner is a blimp.

Another 2009 study found that a one-pound increase in the weight of the average car occupant drives up gasoline demand by 40 million gallons per year. To put that in perspective, the researchers calculated that Americans during the Bush II era used an extra 473 million gallons of gas each year compared to predecessors during Bush I, 758 million more than the unhappy ex-hippies of Carter's day, and 1.1 billion more than the trim veterans of the Eisenhower epoch. Imposing as that sounds, we're only talking about 1 percent of gasoline consumed by U.S. autos.

In search of more frightening statistics, we turn to a transportation mode where weight really matters-flying. The Centers for Disease Control put the average weight gain of American adults from the early 1990s to 2000 at 8.5 pounds for men and 11.4 pounds for women. Hurling that bulk through the skies meant burning an additional 350 million gallons of jet fuel costing more than a billion dollars annually.

Let's try greenhouse gas emissions. Yet another 2009 study considered how much extra energy is needed to sustain a fat populace versus a skinny one. Comparing typical average weight distribution in 1970 to now, the researchers calculated that a hypothetical population of 1 billion fat adults contributes to global warming as follows:

• 270 million more metric tons of greenhouse gases stemming from extra food production needed for the 19 percent more calories we'd eat overall.

• 170 million tons of gases due to increased auto fuel consumption.

• 2 million tons for extra plane fuel.

If one assumes obese people mostly live in developed countries using more energy per capita, obesity results in as much as 1 billion extra tons of greenhouse gases per billion population annually. This gives us the desired conclusion: fat people, by their very existence, are imperiling the planet.

The animals and plants required to produce the additional food consumed by an overweight population also boost emissions-worldwide production of animal feed contributes 18 percent of GHG, more than all forms of transport.

Finally, a recent George Washington University study assessed the annual per-person cost of obesity as $4,879 for women and $2,646 for men, mostly due to higher medical costs and lost job opportunities. So listen to what science is telling you, America: don't be fat.